On 21-05-18, 20:56, Frank Mori Hess wrote:> On Mon, May 21, 2018 at 5:16 AM, Vinod Koul <vinod.koul@linaro.org> wrote:> >>> >> I understand the residue can't be read after terminate, that's why> >> reading the residue is step 2 in pause/residue/terminate. My question> >> was whether the entire sequence pause/residue/terminate taken as a> >> whole can or cannot lose data. Saying that individual steps can or> >> can't lose data is not enough, context is required. The key point is> >> whether pause flushes in-flight data to its destination or not. If it> >> does, and our residue is accurate, the terminate cannot cause data> >> loss. If pause doesn't flush, an additional step of flush_sync as> >> Lars suggested is required. So pause/flush_sync/residue/terminate> >> would be the safe sequence that cannot lose data.> >> > I wouldn't use cannot, shouldn't would be better here as it depends on HW and> > where all data has been buffered and if it can be flushed or not.> >> > Have you checked if pl330 supports such flushing?> > It does not, at least in the context of pausing. The dma-330 DMAEND> instruction flushes in-flight data to its destination, and there are> read/write barrier instructions also, but none of them can be injected> on the fly into a running dma thread. DMAKILL can be, but it discards> in-flight data. Currently, if an 8250 serial driver uses the pl330> for rx dma, the result is possible data loss/corruption. If there was> a stronger pause capability, call it "cmd_sync_pause" which guaranteed> flushing of in-flight data to its destination and accurate residue> reading when paused, then the 8250 serial driver could check for> "cmd_sync_pause" and reject dma drivers that do not have that> capability. pl330.c would not advertise cmd_sync_pause. I don't know> if other dmaengine hardware would be able to support cmd_sync_pause or> not, I'm mostly just familiar with the pl330. The ep93xx_dma.c driver> for example has a m2p_hw_synchronize function which seems to do a> flush.

Well looks like even adding support for sync_pause doesn't solve your issue onpl330. Do you want to move this to PIO mode then..?